Garage Conversion Costs and Loan Amounts
The cost of a garage conversion varies depending on whether the garage is integral (attached to and within the footprint of the house), attached (joined to but outside the main footprint), or detached. Integral and attached garage conversions are the most straightforward and cost-effective, as they share one or more walls with the main house and often have existing connections for plumbing and electrics.
A basic integral single garage conversion — insulating the floor, walls, and ceiling, fitting a front wall with a window or glazed door, connecting to the central heating, and plastering and decorating — typically costs £10,000 to £15,000. A more ambitious brief with en-suite shower room, bi-fold doors to the garden, and premium finishes can reach £20,000 to £30,000. A double garage conversion is broadly double these figures, running from £18,000 to £35,000 depending on specification.
For a £15,000 garage conversion funded by a secured loan at 8.5% over 8 years, monthly repayments are approximately £213. Over 12 years at the same rate, repayments reduce to around £167. The difference in total interest paid between these two terms is approximately £2,400, which is a meaningful sum — but the lower monthly payment of the longer term is often worth the marginal extra cost for homeowners managing tight budgets.
It is worth noting that not all garages can be converted. Some garages — particularly those that serve as a structural element of the house above — require significant additional structural work that can raise costs substantially. A structural engineer's assessment (typically £300 to £600) before applying for the loan will confirm the feasibility and any additional cost implications.
Planning Permission and Building Regulations for Garage Conversions
In most cases, converting an integral or attached garage into a habitable room in England does not require planning permission. The change of use is generally considered permitted development, and no external footprint is being added. However, if you are changing the appearance of the front of the property significantly — for example, removing the garage door and replacing it with a window or new wall in a different material — you may need planning consent in certain areas, particularly conservation areas.
A detached garage conversion is more complex from a planning perspective. Converting it into a habitable annexe or separate accommodation requires planning permission as a change of use from outbuilding to residential. This is subject to more scrutiny and is covered in more detail in our guide to secured loans for annexes.
Building regulations approval is mandatory for all garage conversions regardless of planning status, because you are changing a non-habitable space to a habitable one. The regulations cover thermal insulation (Part L), structural adequacy (Part A), fire safety (Part B), ventilation (Part F), and electrical safety. Your contractor should manage the building regulations process and ensure a completion certificate is issued at the end of the project.
Lenders will check that the works were carried out with appropriate permissions. A secured loan lender will typically require confirmation that building regulations approval was obtained and a completion certificate issued. Without this documentation, the conversion may not be recognised as habitable space by future buyers' lenders, which could affect your ability to sell the property.
